Hi!

This patch generates STRD instruction instead of PUSH in thumb2 mode for
A15.

For optimize_size, original prologue is generated for A15.
The work involves defining new functions, predicates and patterns.

The patch is tested with check-gcc, check-gdb and bootstrap with no
regression. 

Changelog entries for the patch for STRD generation for a15-thumb2:

2011-10-11  Sameera Deshpande
<sameera.deshpande@arm.com>                                             
                                                                                                       
        * config/arm/arm.c (thumb2_emit_strd_push): New static
function.  
          (arm_expand_prologue): Update. 
        * config/arm/ldmstm.md (thumb2_strd): New pattern.
          (thumb2_strd_base): Likewise.
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